Search found 2866 matches

by axel_knutt
28 Mar 2024, 4:59pm
Forum: Health and fitness
Topic: Calculate avg speed on a flat ride
Replies: 8
Views: 172

Re: Calculate avg speed on a flat ride

uhhu wrote: 28 Mar 2024, 11:50amHow can I roughly calculate my avg speed on a flat based off of a recent ride which has elevation?
If you've already got a load of data on Strava that you can cut & paste into Excel, it's simple enough to calculate your own personal "Naismith's Rule" if you download the regression add-in.
by axel_knutt
28 Mar 2024, 11:13am
Forum: Campaigning & Public Policy
Topic: Over-powerful LED lights
Replies: 101
Views: 6702

Re: Over-powerful LED lights

1. I wonder whether police stats are sufficiently detailed to reveal an effect that my be small in terms of all-cause road deaths but quite large in terms of deaths related to headlamp design. I also think that any advantage of better visibility will have been consumed in the form of faster driving rather than reduced accident rate, and that that possibility won't have been researched.

2. There is no sharp binary boundary at the edge of the beam pattern, lamps that are brighter in the middle of the beam will also be brighter at the margins.

3. Degree of dazzle doesn't just depend on the location of the viewer relative to the beam, it also depends on the direction of the viewer's gaze. From any given position, you may be able to see to the side, but the vicinity of the car with the offending lights is obscured, and that makes it difficult to be sure of avoiding hitting it. If you increase the brightness within the beam too much when the light level around the car remains unchanged then this difference will exceed the dynamic range of the eye.

4. I didn't know that the UN had a finger in the vehicle regulation pie, considering that we left the EU so that we don't have to be told what to do by forriners, it's interesting that we're happy to be involved with them. Mr. Konstantin Glukhenkiy is the contact, I wonder if he's amenable to submissions from lay road users.
by axel_knutt
26 Mar 2024, 4:55pm
Forum: Campaigning & Public Policy
Topic: "Why is the right at war with cyclists?... "
Replies: 26
Views: 1275

Re: "Why is the right at war with cyclists?... "

Jdsk wrote: 25 Mar 2024, 9:12pm "Why is the right at war with cyclists? We’re not ‘wokerati’ – we’re just trying to get around":
https://www.theguardian.com/commentisfr ... get-around

Jonathan
It's not about cyclists, it's motorists. Here's how they react when they're held up by road works. I recall a similar article about tractor drivers not so long ago.
by axel_knutt
26 Mar 2024, 4:48pm
Forum: Campaigning & Public Policy
Topic: "Why is the right at war with cyclists?... "
Replies: 26
Views: 1275

Re: "Why is the right at war with cyclists?... "

a.twiddler wrote: 25 Mar 2024, 10:52pmAbove all don't dare to stand up for your rights, you'll be labelled as a trouble maker.
Really? You don't say.
a.twiddler wrote: 25 Mar 2024, 10:52pmIt's got all the sophistication of the school playground, bashing those who are identifiably different from the herd to distract from the failure of those who supposedly, aren't.

It's an old old technique, yet people still seem to fall for it. It's not just cyclists getting "othered".
Indeed.
by axel_knutt
25 Mar 2024, 6:33pm
Forum: Health and fitness
Topic: Why are the general population resistant to getting fit?
Replies: 97
Views: 5027

Re: Why are the general population resistant to getting fit?

ANTONISH wrote: 25 Mar 2024, 9:52amHe told me that his father and uncle never took any exercise and spent a lot of their later years sitting in armchairs - both living into their nineties.
In the same way that some smokers don't get lung cancer?
by axel_knutt
24 Mar 2024, 1:34pm
Forum: Campaigning & Public Policy
Topic: Over-powerful LED lights
Replies: 101
Views: 6702

Re: Over-powerful LED lights

Diatom wrote: 24 Mar 2024, 12:49pmreport on blinding car lights ( https://www.theaa.com/about-us/newsroom ... headlights )
"27% say the design of brake lights on cars are ‘more style over substance’"
This is a problem in general, not just with lights, or even just cars. These days the design of almost everything is mainly determined by what makes a winning marketing gimmick, and less and less by what's safe, or practical to use, or even useful. Another example would be the touch screens that take 30 seconds of searching in a menu to find something you could previously reach out and feel for without even taking you eyes off the road. Even when there is a prima facie reason to suppose that something has a safety benefit, there's scant regard payed to investigating the possibility that its presumed benefit may be completely undermined by risk compensation in practice before it gets put into production.

"there is an acceptance that having brighter lights is better for road safety"
Better at shifting responsibility from those who want to drive faster onto those who are dazzled by the lights.
by axel_knutt
20 Mar 2024, 2:23pm
Forum: Health and fitness
Topic: Atrial Fibrillation...Should We Worry
Replies: 102
Views: 13122

Re: Atrial Fibrillation...Should We Worry

Jdsk wrote: 20 Mar 2024, 1:14pmradiofrequency point‑by‑point ablation should be considered in people with symptomatic paroxysmal atrial fibrillation if drug treatment is unsuccessful, unsuitable or not tolerated
I can do nothing but sit in this chair all day and every day, it's ruining my life. That wasn't the case when they offered it to me in July 2013.
by axel_knutt
20 Mar 2024, 12:44pm
Forum: Health and fitness
Topic: Atrial Fibrillation...Should We Worry
Replies: 102
Views: 13122

Re: Atrial Fibrillation...Should We Worry

brianleach wrote: 20 Mar 2024, 7:19amI was only offered 1 ablation and my cardiologist expressed some surprise that I had stayed in SR for longer than he expected after that ablation.
I was offered an ablation for my AF ten years ago, and I'm still waiting for it.
by axel_knutt
20 Mar 2024, 12:05pm
Forum: The Tea Shop
Topic: Food poverty-the way out
Replies: 756
Views: 27925

Re: Food poverty-the way out

simonineaston wrote: 20 Mar 2024, 11:40am What exactly is there to be happy about? Let's recall that our primate brains are inclined towards two overarching tendancies - opportunism and optimism. Thus any thoughts we have will tend to err on the side of imagining that 'it will be alright on the night'... the likeilhood is that it won't and anyone with half an ounce of sense should have realised that by now.
Off for a nice restorative cycle ride now :-)
Depressive Realism: The perception and judgment of depressed people tends to be more accurate because they are less prone to self-serving bias.
by axel_knutt
19 Mar 2024, 6:02pm
Forum: Health and fitness
Topic: Atrial Fibrillation...Should We Worry
Replies: 102
Views: 13122

Re: Atrial Fibrillation...Should We Worry

Psamathe wrote: 12 Dec 2023, 4:09pmlying on my left side makes it a lot worse
Very common.

In the days when I could shrug off my AF I didn't take much notice, but since my AF got much worse in 2020 I've had to sleep on my right side only for about the last two years because it's completely intolerable otherwise.
brianleach wrote: 19 Mar 2024, 4:01pmI still think 2 ablations isn't a good sign.
It's fairly common to need 2 or even 3 for AF, and then a PVI is only about 70% successful IIRC. On the other hand, a CTI for atrial flutter is much quicker, simpler, and higher success rate though.
by axel_knutt
19 Mar 2024, 2:25pm
Forum: Bikes & Bits – Technical section
Topic: SKS Chainbow?
Replies: 26
Views: 1654

Re: SKS Chainbow?

Tucking trousers into socks is no use, when I bend my legs the bottoms of my trousers ride up above the top of my socks. Cycle clips aren't much fun either unless I want them around my calves.

Before I switched to Ron Hill Bikesters, I used polycotton walking trousers, and modified a pair for cycling in. They had a zip across each leg just above the knee with a gusset sewn in behind, so that when I got on the bike I opened the zip and the gusset allowed the leg to bend without riding up. I then had tabs with Velcro sewn on the bottoms like the ones on waterproof over trousers. Very convenient, but it takes a bit of time to make them.

I had a strong wind from the front right quarter blow my Lycra Bikesters into the chainring once.
by axel_knutt
19 Mar 2024, 10:49am
Forum: Bikes & Bits – Technical section
Topic: how slow do they get?
Replies: 17
Views: 1103

Re: how slow do they get?

Given that 'unpunctured' tyres still go flat eventually, it begs a definition of what constitutes a puncture.
by axel_knutt
18 Mar 2024, 6:52pm
Forum: The Tea Shop
Topic: Heat in the home
Replies: 2297
Views: 134356

Re: Heat in the home

axel_knutt wrote: 16 Jan 2024, 5:39pmI measured the cost of running the heating continuously a few years ago, and found that switching off for 7 hours overnight saved about 12% off the gas consumption.
I think I must have been typing that from memory instead of checking.

So, the first time I measured this was for 8 weeks in November and December 2017, and alternated the heating between timed and continuous each week to minimise the effect of weather, on the basis that any temperature variations won't be synchronised with the measurement periods. Comparing the ratio of average fuel consumption to average temperature difference for the 4 timed weeks and 4 continuous weeks, I got a 7.9% (not 12%) reduction in consumption with the heating switched off at 00:30, and back on again at 07:30.

This winter I repeated the measurement but by a different method: running the heating continuously for the whole winter and comparing it with the timed running during the three preceding winters. To account for variations in the weather, this time I normalised the fuel use to the heating load in degree days. The result this time was an average consumption of 350W/K on timed, and 383W/K on continuous, giving a similar saving of 8.5%. (Heating load measurement)

I also have a model of the house and heating system on the computer (in the form of a virtual analog computer running on Spice), so I thought it would be interesting to compare what that says against the actual measurements. This time I don't need to worry about the effect of weather variations, because I can repeat the simulation with exactly the same weather temperature for both timed and continuous operation. The result I got this time was a saving of 9.47% using weather data for Oct 2021 and 9.53% for Jan 2022, those months being chosen so as to cover a wide range of heating loads.

In view of the similarity of the results for all three measurement methods, I think it likely that the results are about correct.

------------ooo-----------
roubaixtuesday wrote: 16 Jan 2024, 6:30pm
axel_knutt wrote: 16 Jan 2024, 5:39pm

roubaixtuesday wrote: 15 Jan 2024, 7:54pmThermal diffusivity is a material property. It tells you almost nothing about how a building responds to temperature changes.

A wall constructed of a single sheet of paper and a wall constructed of 10 metre wide coastal redwood trunks would have the same thermal diffusivity.
Thermal diffusivity is absolutely fundamental: it’s what determines how fast a material can change temperature in response to a change in surrounding temperature, and how fast a change in temperature can propagate from one side of it to the other. What I said above all assumes a static system, but the conditions never are static: as weather and/or heating level change the thermal diffusivity of the walls determines how fast they can follow, and hence the extent to which MRT and level of radiant asymmetry vary, causing transient variations in thermal comfort.

If you believe thermal diffusivity is "absolutely fundamental" please answer the point about how it is identical for walls regardless of their thickness.

It is a property of a material, not a property of a building, or even an element of a building.

In the same way that the performance of bicycle frame depends on it's geometry, tube thickness and other design parameters, not just the youngs modulus of the material.
Diffusivity is a property that's normalised to a standard dimension, in the same way that density is weight normalised to a standard volume. What you are arguing is the equivalent of saying that the density of steel has no effect on the weight of a bike because it's just a property of the material, or that the contents of your bath weigh the same as the contents of the local reservoir because the density of the water is the same in both.

One advantage of computer models is that you can test hypothetical what-ifs that wouldn't otherwise be possible:
With & Without Inertia Jan 2022.png
On the left, the inside and outside temperatures from data logging thermometers are plotted in green and blue respectively, and in red you can see that the modelled inside temperature is a reasonably good fit for the measured data. On the right is the same plot again, but this time it shows the result when I remove all the thermal inertia from the model: unsurprisingly the temperature plummets as soon as the heating switches off, because there's no longer any heat capacity in the building to maintain it.

We can also look at how the thermal properties of the wall affect the heat transfer through the wall:
Cavity Wall Surfaces.png
Here, the red trace is internal air temperature, and then from top to bottom are the temperatures of the internal surface of the internal leaf of the cavity wall, the external surface of the internal leaf, the internal surface of the external leaf, the external surface of the external leaf, and finally, the outside air temperature in blue, which I've set to be constant so as not to obscure the effect we're looking at.

What you can see is that the thermal resistance and heat capacity of the brickwork combine to create a low-pass filter, smoothing out the temperature variations between the inside and outside of the wall. Note that not only has almost all of the temperature variation gone, but there's a phase shift: minimum temperature on the inside occurs at 07:30, immediately before the heating comes back on, but the outside surface of the wall doesn't reach minimum temperature until gone midday. All this effect disappears if you don't take proper account of the way that the thermal resistance and heat capacity combine to influence the way that heat diffuses through the wall.

The reason I built the model in the first place is that I was interested in exploring the transient effects as the heating switches on and off.
Jdsk wrote: 17 Jan 2024, 12:13pm
axel_knutt wrote: 16 Jan 2024, 5:39pm ...
If the walls of a room were at body temperature, then the radiant heat passing from the body to the walls would be exactly balanced by the heat radiated from the walls to the body. Walls colder: there’s a net heat loss, hotter and there’s a net heat gain.
...
I'm all in favour of thought experiments in discussing the physics.

But in this one is there any heat flow from the interior surface of the walls to the walls and the outside world? And is there any conduction and convection within the room?

Thanks

Jonathan
I don't see what you're getting at, I haven't said that there's no convection or conduction in the room, and I don't see the relevance of conduction through the wall. The point I was talking about is that people are more sensitive to radiant heat, and that asymmetric radiation causes thermal discomfort. Radiant heat's not irrelevant, or even insignificant.

See here:
Asymmetric Radiation.png
An excessively warm ceiling is the most uncomfortable, followed by a cool wall (which is the problem I have in my dining room).
by axel_knutt
17 Mar 2024, 3:06pm
Forum: Campaigning & Public Policy
Topic: LTN politics
Replies: 54
Views: 3589

Re: LTN politics

The review was published this morning.
https://www.gov.uk/government/publicati ... ood-review
by axel_knutt
17 Mar 2024, 1:23pm
Forum: The Tea Shop
Topic: Just how long will it take to turn this ship around?
Replies: 103
Views: 2926

Re: Just how long will it take to turn this ship around?

Pebble wrote: 17 Mar 2024, 12:46pmif that happens we will flounder on the rocks, we're in treacherous waters
Keir Starmer needs to steer calmer waters?